Rendering to Google Drive?
No, you can not use environment variables in the Output File field, because it doesn't support drivers (and key-framing also).

You would have to write a python script that would change this field every time you open the file (with Run Python Scripts enabled in Preferences). In the script you can for sure use python environment variables:

import bpy
import os

user = os.environ['USERNAME']
bpy.context.scene.render.filepath = "C:\\Users\\" + user + "\\GoogleDrive\\file_name"




The best thing to do is to put the .blend file also in the Google Drive folder and use relative paths just like: //rendered\file_name(this saves to folder "rendered" next to the .blend file).